Various types of filters are known for filtering water and similar liquids. A particularly useful type of filter is a disk filter. Filters of this type are described and claimed, for example, in applicant's U.S. patent applications Ser. Nos. 647,094, filed Sep. 4, 1984, which is now U.S. Pat. No. 4,624,785; 709,371, filed Mar. 7, 1985, which is now abandoned; 709,372, filed Mar. 7, 1985, which is now U.S. Pat. No. 4,683,060; 709,373, filed Mar. 7, 1985, which is now U.S. Pat. No. 4,654,143; and U.S. Pat. Nos. 4,026,806; 4,042,504; 4,045,345; 4,271,018; 4,278,540; 4,295,963.